Voltage regulator



Jan. 5, 1965 T. B. GIBBS VOLTAGE REGULATOR Filed Dec. 14, 1959 I 2 U 4 h. w 7J2 E12 2 I! 7 0 w Th ow 9 a iTlT a w w 3 v a f Ti 1 3m 1 0 a, a m/ United States Patent Ofifice 3,164,660 Patented J an. 5, 1965 This invention is concerned with a regulated power supply particularly designed for energizing the tone generator Circuitry of an electronic musical instrument.

The tone generators of certain types of electronic musical instruments are sensitive to variations in the energizing voltage resulting in corresponding variations in the amplitude of the generated tones. This is particularly noticeable in a tone generator system where the amplitude of current drawn from the power supply is dependent upon the number of tones sounded simultaneously, the output potential of the power supply decreasing with an increase in current drain. The striking of a chord substantially increases the current drain on the power supply and the correseponding decrease in output potential causes a marked diminution in the amplitude of a generated tone being sounded at the same timeQ The present invention provides a regulatory circuit specifically designed for the power supply from which the tone generators of an electronic musical instrument are energized.

One feature of the invention is the provision of a source of potential for energizing the lamps of a light responsive tone generator having meansassociated with the source for regulating the amplitude of the output potential to maintain the intensity of the, light from the lamp substantially constant. In particular, a saturable reactor'has a controlled winding connected with the input to the poten tial source and a control winding responsive to the amplitude of current drawn from the source.

Another feature is that the power supply has two sections, providing potentials of differing amplitude one for bass or pedal notes and the other for treble notes, with the regulation of the potentials controlled as a function of the total current drawn from both sections.

Still a further feature is that loads independent of the tone generator circuitry are connected with the source of potential providing a minimum load thereon and minimum control'current for the saturable reactor.

Further features and advantages of the invention will readily be apparent from the following specification and from the drawing which is a schematic representation of an embodiment of the invention.

In one type of light sensitive tone generator for an electronic musical instrument'a lamp illuminates an area of a mask plate which area has a configuration related to the tonal quality or harmonic content of the note'to be sounded, and the lighted area is scanned through a narrow slot at a rate which determines the frequency of the generated tone. The scanned light acts on a photocell to establish an electrical signal representing the desired tone. In one specific musical instrument incorporating this type of tone generating system twelve tone generators are provided, one for each of the twelvenotes in an octave. Each tone generator includes a mask and scanning assembly arranged to generate tones of differing tonal compo- I keys actuated concurrently, while the accompaniment con-" sists primarily of chords which may require three or four notes to be sounded simultaneously on a manual keyboard and a further note in the pedal section. In the instrument of the aforementioned type, a cold lamp has a rather low resistance and when several cold lamps are energized simultaneously, the drain on the power supply is such that the output potential drops appreciably. If a note of the melody is being sounded when a change is made in a chord combination, an appreciable variation in amplitude of the melody occurs, which is highly undesirable. Similarly, when a multiple note chord is released the output potential of the power supply increases causing an audible increase in amplitude of a melody note being sounded.

The novel regulated power supply disclosed herein overcomes these objections and provides a circuit for energizing the lamps of a tone generating system in which a regulatory effect is based on the amplitude of the lamp current drawn by the system. In the drawing terminals 1 and 2 are connected with a suitable source of energizing potential, as volt alternating current which is thus connected with the primary winding 3a of a power transformer 3, through the controlled windings 4a of a saturable reactor 4. Secondary winding 31) of power transformer 3 has a center tap 5, a first pair of intermediate range taps 6a and 6b providing a first secondary potential and a pair of terminals 7a and 7b providing a second and higher secondary potential. A pair of rectifiers 8a and 8b are connected with terminals 6a and 6b providing full wave rectification at the first potential. Connected with rectifiers Strand 8]) is an inductor input filter network including series inductors 9 and 10 and shunt capacitors 11 and 12 The output otthis section of the power supply appears across terminals 13 and 14 of which terminal 13 is connected to a common or ground reference 15, with terminal 14 being positively phased with respect to terminal 13. A g I A second set of rectifiers 15a and 15b are connected with terminals 7a and 7b of secondary winding 31) of the transformer providing full wave rectification of the second and higher output potential. Again, an inductor input filter includes series inductors 16 and 17 and shunt capacitors 18 and 1 9. The output of the second section of the power supply is obtained between terminals 20 and 14,

with terminals'Zt) being negative with respect to terminal 14 and having an amplitude greater than the potential ap pearing between terminals 13 and 14. For example, in

instrument and connected between terminals 20 and 14.

The load 24 is connected across terminals 13 and 14 and in parallel with lamps 22. A further load 25 is con nected from a point between the inductors 9 and 10 of the filter ofthe first section of the power supply and terminal 14. A

The line 26 connected with the terminal 14 is a common return line for the entire power supply and all of the current drawn from the power supply flows through conductor 27 connected from line 26 and through con trol winding 4b of saturable reactor 4 to center tap 5 of secondary winding 3b of the power input transformer. Thus, the impedance of the saturable reactor 4, which is connected in series with primary winding 3a of the'power transformer, is a function of the total current drawn from the power supply. With a low or minimum current draw,

the impedance of saturable reactor-4 is at a maximum and as the current drawn increases the impedance drops,

simultaneously increasing the voltage applied to the primary winding 3a of the power transformer and thus the eiiective potential of the power supply, compensating for the output voltage drop with increased load. When the load current decreases, the impedance of reactor 4a increases reducing the voltage to transformer 3 and keeping the power supply output potential relatively constant.

The stable operating point of the system is established by the normal steady state current delivered by the power supply, which includes the current to load 24, and the current drawn through a bleeder resistor 23 connected between terminals 20 and 14 providing a minimum load on the second section of the power supply. With this system the surge current drawn by several cold lamps connected in the circuit simultaneously provides an increased input potential compensating for the increased internal voltage drop in the power supply without any appreciable diminution in the tone of a note being sound-' ed. Similarly, when a chord is released, the drop in current through the system increases the impedance of saturable reactor 4 decreasing the voltage applied to primary winding transformer 3 and effectively dropping the input potential slightly.

, While I have shown and described certain embodiments of my invention, it is to be understood that it is capable of many modifications. Changes therefore, in the construction and arrangement may he made without departing from the spirit and scopeof the invention as disclosed in the appended claims.

I claim:

1. In an electronic musical instrument having light responsive tone generating means including a plurality of groups of lamps, the amplitude of the tone representing electrical signal generated being a function of the intensity of light from said lamps, a power-supply comprising: a source of a plurality of potentials for energizing of a respective group of lamps, the lamps of each group being selectively connectable with a respective potential; means connected to said source for deriving a potential opposite to each of said plurality of potentials and responsive to the amplitude of current flowing through all of said lamps for regulating the amplitude of said potential to each group for maintaining the intensity of light from each lamp substantially constant; and a bleeder associated with one of said potential outputs for maintaining a minimum control current flow.

2. In an electronic musical instrument having light responsive tone generating means including a plurality of lamps, the amplitude of the tone representing electri- 'with the primary of the transformer and having a control winding; rectifier means connected with each of the outputs, the secondary of the transformer providing a a plurality of unidirectional sources of potential for said lamps, the lamps in each of a plurality of groups being selectively connectable with a respective one of said sources; and a return' circuit for lamp current completed through the control winding of said saturable reactor to said secondary for regulating the amplitude of said unidirectional potential in accordance with the current through all the lamps to maintain the intensity of light from each lamp substantially constant.

3. In an electronic musical instrument having light responsive tone generating means including a group of manual section lamps and a group of pedal section lamps the amplitude of the tone representing electrical signal generated being a function of the intensity of light from said lamps, a power supply comprising a power transformer having a primary winding and having a secondary winding with a center tap, a pair of intermediate taps forming a first output, and a pair of outer taps forming a second output producing a higher potential than the first output, a saturable reactor having a controlled winding connected in series with the primary winding of the transformer and having a control winding connected to the center tap of the secondary winding, first and second rectifier means connected respectively to the intermediate and outer taps of the secondary winding, the manual section lamps being connected to the first rectifier means and the pedal section lamps being connected to the second rectifier means for energization by a higher source of potential than the manual section lamps, both groups of lamps being connected to the control winding of the saturable reactor regulating the amplitude of the unidirectional potential in accordance with the current through all of the lamps to maintain the intensity of light from each lamp substantially constant, and a load of substantially constant magnitude connected to one of the sources of potential to stabilize the operation of the power supply. I

4.. The power supply claimed in claim 3 together with filters connected between the rectifier means and their respective lamps.

References Cited in the file of this patent UNITED STATES PATENTS 2,169,842 Kannenburg Aug. 15, 1939 2,733,402 Bixby Jan. 31, 1956 2,752,551 Bixby June 26, 1956 2,802,166 Sanderlin et al. Aug. '6, 1957 2,858,499 Silver Oct.28, 1958 2,941,434 7 Clark June 21, 1960 FOREIGN PATENTS 144,469 Sweden Mar. 16, 1954 211,836 Australia Nov. 28, 1957 OTHER REFERENCES Saturable Reactor Control of Full Wave and l3i-Phase Rectifier, American Institute of Electrical Engineers, Dec, 17, 1958, Paper No. Cl 59-223. 

1. IN AN ELECTRONIC MUSICAL INSTRUMENT HAVING LIGHT RESPONSIVE TONE GENERATING MEANS INCLUDING A PLURALITY OF GROUPS OF LAMPS, THE AMPLITUDE OF THE TONE REPRESENTING ELECTRICAL SIGNAL GENERATED BEING A FUNCTION OF THE INTENSITY OF LIGHT FROM SAID LAMPS, A POWER SUPPLY COMPRISING: A SOURCE OF A PLURALITY OF POTENTIALS FOR ENERGIZING OF A RESPECTIVE GROUP OF LAMPS, THE LAMPS OF EACH GROUP BEING SELECTIVELY CONNECTABLE WITH A RESPECTIVE POTENTIAL; MEANS CONNECTED TO SAID SOURCE FOR DERIVING A POTENTIAL OPPOSITE TO EACH OF SAID PLURALITY OF POTENTIALS AND RESPONSIVE TO THE AMPLITUDE OF CURRENT FLOWING THROUGH ALL OF SAID LAMPS FOR REGULATING THE AMPLITUDE OF SAID POTENTIAL TO EACH GROUP FOR MAINTAINING THE INTENSITY OF LIGHT FROM EACH LAMP SUBSTANTIALLY CONSTANT; AND A BLEEDER ASSOCIATED WITH ONE OF SAID POTENTIAL OUTPUTS FOR MAINTAINING A MINIMUM CONTROL CURRENT FLOW. 